Adaptability of <i>Moringa oleifera</i> Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes

doi:10.4236/ajps.2011.26092

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American Journal of Plant Sciences, 2011, 2, 776-780

doi:10.4236/ajps.2011.26092 Published Online December 2011 (http://www.SciRP.org/journal/ajps)

Adaptability of Mor in ga ol eif er a Lam.

(Horseradish) Tree Seedlings to Three

Temperature Regimes

Quintin E. Muhl, Elsa S. du Toit, Petrus J. Robbertse

Department of Plant Production and Soil Science, University of Pretoria, Pretoria, South Africa.

Email: [email protected]

Received August 12th, 2011; revised September 22nd, 2011; accepted October 24th, 2011.

ABSTRACT

Moringa oleifera trees are naturally found in tropical climates around the world, while the extent of their adaptability

to cooler climates was the main ob jective of this stud y. A total of 264 trees, made up of an equal number hardened and

non-hardened seedlings were randomly assigned to three temperature-controlled greenhouses each with a different

fluctuating night/day temperature regime (TR) namely; 10/20˚C ± 2˚C, 15/25˚C ± 2˚C and 20/30˚C ± 2˚C. During the

32-week trial period, biweekly measurements of tree height, stem diameter and leaf area estimates of each individual

tree within all three temperature regimes (TRS) were taken. The 20/30˚C TR was the most favorable towards overall

tree growth, as the highest values were obtained across most measured parameters. The increase in temperature re-

sulted in growth rate increases of over 650% between the 10/20˚C and 20/30˚C and over 250% between the 10/20˚C

and 15/25˚C night/day TRS. The hardening-off pre-treatment increased both final tree height and stem diameter, re-

sulting in increases of 3.09 × (10/20˚C), 1.44 × (15/25˚C) and 1.23 × (20/30˚C) compared to their non-hardened off

counterparts. Although the average leaf area increased with the increase in TR and remained higher for the duration of

the trial, cycles of regular leaf drop and renewed flushes were prevalent at both the 15/25˚C and 20/30˚C temperature

treatments.

Keywords: Hardening - Off, Biodiesel, Growth Rate

1. Introduction

Moringa oleifera Lam. also known as Horseradish tree is

one of 14 different species belonging to the family Mor-

ingaceae. Although indigenous to the sub-Himalayan re-

gions in northwestern India, it is currently found in nu-

merous countries situated in the tropical and sub-tropical

regions across Africa, South East Asia and South Ame-

rica (Jahn, 1988) [1]. M. oleifera is a fast growing, small

to medium sized tree ranging between 5 to 12 m in

height. The tree is evergreen in tropical, while deciduous

in sub-tropical climates. The tree canopy has an umbrella

shaped crown with bi-(tri-)pinnate leaves, while the indi-

vidual leaflets have a leaf area of one to two cm2. Flo-

wers are white to cream colored and zygomorphic. The

tree bears 20 to 30 cm long fruit that once mature,

change colour from green to brown revealing numerous

round or triangular seeds with three papery wings (Fol-

kard, et al., 1999) [2]. Amongst the most common uses

for M. o leifera such as animal forage, nutrition, medicine

and water purification, the seed also contains a multi-

purpose, non-drying oil. One of the uses for this oil is the

production of biofuel, in the form of biodiesel (Rashid et

al., 2008) [3]. Biodiesel is a renewable fuel source that is

obtained through the process of transesterification where

natural plant oils are transformed into a fuel, which can

be used in conventional diesel engines (Poeet, 2006) [4].

Since M. oleifera plantations of 3270 trees/ha can yield

anything between 991 - 3303 liters of oil per hectare, de-

pending on the soil and environmental conditions, it can

effortlessly compete with several other oil crops in terms

of liters of oil per hectare (Fuglie, 2001) [5]. Although M.

oleifera is grown throughout numerous African countries,

no evidence of large-scale commercial plantings have

been reported, possibly as a result of the limited scien-

tific data that is currently available on both the propaga-

tion and cultivation of the tree.

Adaptability of Moringa oleifera Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes777

2. Materials and Methods

Growth performance trials were conducted at Phytotron

Section on the Experimental Farm of the University of

Pretoria (25˚45′S, 28˚16′E) at an altitude of 1372 m

above sea level.

Trees for the purpose of this trial were grown from

seeds sourced from wild M. oleifera trees in Malawi.

Seeds were planted and germinated in seedling trays con-

taining Hygromix™, a sterile, soilless growing medium

for seedlings, manufactured by Hygrotech Seed (Pty) Ltd.

After germinating seed under favorable green-house con-

ditions between 20˚C - 25˚C for one week, half the seed-

lings were left in the greenhouse, while the other half

was hardened-off by placing them outside where the av-

erage minimum/maximum temperatures fluctuated be-

tween 15/30˚C. Both treatments were irrigated to field-

capacity every second day. Equal numbers of hardened-

off (132) and non-hardened-off (132) seedling-trees were

randomly selected and transplanted into 10 liter black

plastic bags, five weeks after seed was planted into seed-

ling trays. These bags were filled with a commercial bark

potting medium manufactured by Braaks (Pty) Ltd. Trees

were placed onto benches inside temperature-controlled

greenhouses. The abovementioned 264 trees were equally

divided and randomly assigned to three different tem-

perature regimes TRS namely, 10/20˚C ± 2˚C, 15/25˚C ±

2˚C and 20/30˚C ± 2˚C, simulating night/day tempera-

ture fluctuations and exposed to natural daylight. The

average photosynthetic active radiation (PAR) at 12:00

in the afternoon on a clear day, inside the temperature-

controlled greenhouses was measured at 1350 µmol·m–2·s–1.

To adjust nitrogen deficiencies evident from soil analysis

results, 20 g of LAN (28) fertilizer was applied to each tree,

16 weeks after trial commencement. Irrigation was manu-

ally applied three times a week until field-capacity was

reached, as the excess water was able to drain from bags.

Bi-weekly measurements of tree height (mm), meas-

ured with a measuring tape and stem diameter (mm),

measured at soil level with a calliper were made of each

tree for the duration of the 32-week trial.

The total leaf area estimates of each tree were calcu-

lated according to a non-destructive method of leaf area

index (LAI) calculation described by Siegfried et al.

(2007) [6]. Firstly, the number of tripinnate leaves as

well as the number of leaflets on the youngest mature

leaf of each tree was counted. Secondly, the number of

leaflets per leaf was multiplied with the number of leaves

per tree to provide an estimate for the number of leaflets

per tree. Then, leaflets were randomly sampled from the

three temperature treatments and measured with a LI-

3100, Licor leaf area meter to provide an estimated leaf

area (cm2) of the individual leaflets. Finally the average

leaf area of a single leaflet was multiplied with the esti-

mated number of leaves per tree to provide an approxi-

mate leaf area per tree.

Data collected over the 32-week trial period were sta-

tistically analyzed using the Statistical Analysis System

(SAS Version 9.1) program for Microsoft Windows, by

the Statistics Department at the University of Pretoria.

The Analysis of Variance (ANOVA) was performed, to-

gether with F-test (Steele and Torrie, 1980) [7] to en-

able the comparison between treatment means.

3. Results and Discussion

The difference in average tree height and stem diameter

of both hardened-off (HO) and non-hardened-off (NHO)

trees within each temperature regime (TR) for the 32-

week trial duration is illustrated in Figure 1. Amongst

the three TRS investigated in this trial, the 20/30˚C TR

clearly was the most favorable for tree growth, with a

final average tree height of 1970 mm and stem diameter

of 28.4 mm. Growth at the 15/25˚C TR was significantly

less with a final average tree height and stem diameter of

1100 mm and 16.1 mm respectively. The 10/20˚C regime

was certainly not conducive to M. oleifera growth as

hardly any noticeable growth occurred throughout the

32-week period. This TR limited the average final tree

height to 480 mm and stem diameter to 8.8 mm. The

effect of the fertilizer application during week 16 was

responsible for the sudden change in growth line gradient.

It is also noticeable how fertilizer use efficiency varied

between the three TRS, while the increase in growth rate

was highest at the 20/30˚C regime, the 10/20˚C regime

revealed only a slight increase in response to the fertil-

izer application (Figure 1).

The final growth between the HO and NHO seedlings

at all three TRS for both the tree height as well as the

stem diameter was not significantly different (Figure 1).

However, the growth rates between the HO and NHO

seedlings for both these parameters differed among and

within the three TRS as illustrated in Table 1. In addition

the percentage increase in growth rate, increased with a

decrease in TR, exemplifying the importance of harden-

ing off seedlings especially if seedlings are to be trans-

planted into a cooler climate. Regardless of the final

growing climate, the HO seedlings are at an advantage

and therefore the hardening-off process is highly rec-

ommended for M. oleifera trees.

The hardening-off process involves several complex

processes that have an effect on numerous morphological

and physiological mechanisms enhancing plant growth

under unfavorable environmental conditions (Villar-

Salvador et al., 1999) [8]. Amongst numerous other

plants, the effect of hardening seedlings prior to trans-

planting were studied on Rosmarinus officinalis and Ne-

rium oleander by Sánchez-Blanco et al. (2004) [9] and

Adaptability of Moringa oleifera Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes

778

Figure 1. Differences in average tree height (cm) and stem diameter (mm) of Moringa oleifera cultivated from both hard-

ened-off and non-hardened-off seedlings at various temperature regimes over a 32-week period. Vertical bars represent LSD.

NHO—non-hardened-off, HO—hardened-off, TH—tree height and SD—stem diameter.

Table 1. Differences in average growth rate (mm/week) between the temperature regimes and hardening-off treatments over

the 32-week trial period. Different letters indicate significant differences at P ≤ 0.05 according to the F-test. NHO—non-hard-

ened-off, HO—hardened-off.

Growth rate (mm/week)

Pre-treatment 10/20˚C 15/25˚C 20/30˚C

Tree height Stem diameter Tree height Stem diameter Tree height Stem diameter

NHO 4.33a 0.11g 18.86c 0.28i 52.94e 0.63k

HO 13.36b 0.21h 27.12d 0.33j 65.08f 0.73l

Average 8.85ab 0.16gh 22.99cd 0.30ij 59.01m 0.68n

Adaptability of Moringa oleifera Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes779

Bañon et al. (2006) [10] respectively. Both these papers

reported the superiority of the hardened (HO) plants over

their non-hardened (NHO) counterparts upon the expo-

sure to unfavorable environmental growing conditions

(Sánchez-Blanco et al. 2004 [9]; Bañon et al. 2006 [10]).

The growth rates between the various TRS, as shown

in Table 1, were significantly different (P ≤ 0.05), in

which a 10˚C increase between the 10/20˚C and 20/30˚C

in the night/day TR caused a tree growth rate increase of

over 650% in tree height and 400% in stem diameter.

While the 5˚C difference between the 10/20˚C and 15/

25˚C TR resulted in a tree height and stem diameter

growth rate increases of over 250% and 200% respec-

tively. The increase in vegetative growth of M. oleifera

trees brought about by the increase in TR agrees with

similar observations made in several other tropical and

subtropical trees (Menzel and Paxton, 1985 [11]; Troc-

houlias and Lahav, 1983 [12]; George and Nissen, 1987

[13]; Utsunomiya, 1992 [14]), such as mango (Whiley et

al., 1989 [15]), macadamia (Lahav and Trochoulias, 1982

[16]) and lychee (Menzel and Paxton, 1985 [11]).

According to Downs and Hellermers (1975) [17], tem-

perature affects both physical and metabolic processes

within plants, by altering the reaction rates of enzyme

systems, since the optimum temperatures for enzymatic

reactions are enzyme specific, and only vary between

enzymatic systems. The highest growth rates are only

achieved once the environmental temperature coincides

with the requirements of these enzymatic reactions. As

the enzymatic reactions responsible for the processing of

photosynthates are temperature sensitive, growth and de-

velopment are a function of the growing temperature.

Temperature extremes would therefore lead to atypical

and reduced growth.

The optimum TR for the purposes of this study evi-

dently is the 20/30˚C TR, as it produced the highest

growth across all measured parameters. However, ac-

cording to Downs and Hellermers (1975) [17], tropical

trees that reach their maximum cardinal temperature,

often manifest this through rapid stem elongation, thin

leaves and reduced dry matter production at the expense

of reproductive development. Observations of the above

symptoms under the 20/30˚C TR, suggest that any fur-

ther increases in temperature would most likely decrease

growth. Compared to the 20/30˚C TR, growth was sig-

nificantly reduced at the 15/25˚C TR, while hardly any

growth was observed at the low 10/20˚C TR. It can

therefore be assumed that the threshold temperature for

growth of M. oleifera trees is within the 10˚C - 20˚C

range. This not only verifies the fact that M. oleifera fa-

vors tropical growing environments as stated by Morton

(1991) [18] and Mughal et al. (1999) [19], but also de-

monstrates the reluctance of M. oleifera to acclimatize

and generate satisfactory growth under cooler climates.

Similarly to the temperature effect on both tree height

and stem diameter, the average leaf area (cm2) increased

with an increase in TR (Figure 2). However, the increase

in leaf area was less steady, as fluctuations in leaf area

occurred due to repeated cycles of leaf drop followed by

renewed flushes. The extent of these fluctuating leaf area

measurements intensified with an increase in TR and was

the most volatile under the 20/30˚C regime. The 15/25˚C

treatment also showed volatility, but to a lesser extent

than the 20/30˚C treatment. The 10/20˚C was the most

stable, showing a slight but constant increase of leaf area

over the 32-week trial period.

4. Conclusions

Growth of M. oleifera is evidently favoured by high

growing temperature of >25˚C, confirming the prefer-

Figure 2. Increase in average tree leaf area (cm2) of Moringa oleifera trees at three temperature regimes over a 32-week pe-

riod. Treatment means with letters in common are not significantly different at P ≤ 0.05. Vertical bars represent LSD.

Adaptability of Moringa oleifera Lam. (Horseradish) Tree Seedlings to Three Temperature Regimes

780

ence of M. oleifera towards tropical growing environ-

ments. This was confirmed by the temperature treatment

results, where trees at the 20/30˚C TR revealed the high-

est growth rates for both tree height and stem thickening.

In addition, the 20/30˚C temperature treatment, although

variable, consistently had the highest leaf area over the

entire trial period. As the effect of additional, higher TRS

were not investigated in this study, the possibility of im-

proved growth at even higher temperatures cannot be

excluded. Tropical climates are therefore ideal for the

cultivation of M. oleifera, however satisfactory growth

during the hot summer months in sub-tropical climates is

achievable, if the winters are mild, as trees are frost ten-

der. The hardening-off of the seedlings prior to trans-

planting has proven to increase the growth rate of both

tree height and stem diameter across all three TRS. The

hardening off process is highly recommended for M.

oleifera trees, especially if intended cultivation is in be-

low optimal temperature environments.

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